Here's an extended battery. Kind of like a battery case. It's just a huge battery that replaces your built in battery. That way it just increases your battery capacity and forget about it.

Zerolemon 7500mAh White: https://www.amazon.com/dp/B00CXZI3DQ/ref=cm_sw_r_sms_c_api_RWbKxbTP9Y1RF

Zerolemon 7500mAh Black: https://www.amazon.com/dp/B00CXZI3DQ/ref=cm_sw_r_cp_api_RWbKxbTP9Y1RF

Anker 7800mAh: https://www.amazon.com/dp/B00GNQ10VS/ref=cm_sw_r_sms_c_api_mZbKxbK9DWQYK

Anker 5200mAh: https://www.amazon.com/dp/B00CPLMG86/ref=cm_sw_r_sms_c_api_9ZbKxbYSZFBFA

Personally I'd just go with the Anker batteries. They're just cheaper in this case. I've bought stuff from both brands and they're both pretty reliable.